Tiered Tie Plates and Fuel Bundles Using the Same

ABSTRACT

Example embodiments are directed to tiered tie plates and fuel bundles that use tiered tie plates. Example embodiment tie plates may include upper and lower tiered tie plates. Example embodiment tiered tie plates may have a plurality of bosses divided into groups, or tiers, having differing vertical (axial) displacement. Example embodiment fuel bundles may use tiered tie plates such that fuel rods in example bundles may originate and terminate at different vertical displacements, based upon the vertical displacement of the bosses receiving the fuel rods into the tiered tie plates. Optionally, shanks may be used to further vary fuel rod axial displacement and diameter.

This application is a continuation of U.S. patent application Ser. No.12/003,145, filed Dec. 20, 2007, the contents of which are incorporatedby reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Example embodiments generally relate to fuel structures and materialsused in nuclear power plants.

2. Description of Related Art

Generally, nuclear power plants include a reactor core having fuelarranged therein to produce power by nuclear fission. A common design inU.S. nuclear power plants is to arrange fuel in a plurality of fuel rodsbound together as a fuel assembly, or fuel bundle, placed within thereactor core. These fuel rods typically include several elements joiningthe fuel rods to assembly components at various axial locationsthroughout the assembly.

As shown in FIG. 1, a conventional fuel bundle 10 of a nuclear reactor,such as a BWR, may include an outer channel 12 surrounding an upper tieplate 14 and a lower tie plate 16. A plurality of full-length fuel rods18 and/or part length fuel rods 19 may be arranged in a matrix withinthe fuel bundle 10 and pass through a plurality of spacers 15. Fuel rods18 and 19 generally originate and terminate at the same verticalposition, all rods continuously running the length of the fuel bundle10, with the exception of part length rods 19, which all terminate at alower vertical position from the full length rods 18. An upper end plug20 and/or lower end plug 30 may join the fuel rods 18 and 19 to theupper and lower tie plates 14 and 16, with only the lower end plug 30being used in the case of part length rods 19.

As shown in FIGS. 2A and 2B, conventional upper and lower tie plates 14and 16 may be generally solid and flat. A plurality of holes, calledbosses, 25 may receive lower end plugs of all rods in an assembly in thelower tie plate 16. Similarly, a plurality of bosses 25 may receive theupper end plug of all full-length rods in the upper tie plate 14. Partlength rods may not terminate at a tie plate. In this way, upper andlower tie plates 14 and 16 may axially join fuel rods to the fuelassembly and hold fuel rods at a constant and shared axial displacementin the core. Because bosses and corresponding fuel rods may begin and/orterminate at the same axial position within the bundle, fluid flow maybe restricted at these axial positions.

SUMMARY

Example embodiments are directed to tiered tie plates and fuel bundlesthat use tiered tie plates. Example embodiment tie plates may includeupper and lower tiered tie plates. Example embodiment tiered tie platesmay have a plurality of bosses divided into groups, or tiers, havingdiffering vertical (axial) displacement. In this way, bosses may receivefuel rods at varying vertical displacements depending on how the bossesare grouped and displaced. Example embodiment tiered tie plates mayreduce fluid flow pressure drop by increasing the minimum crosssectional flow area available through a fuel bundle.

Example embodiment fuel bundles may use tiered tie plates such that fuelrods in example bundles may originate and terminate at differentvertical displacements, based upon the vertical displacement of thebosses receiving the fuel rods into the tiered tie plates.Alternatively, shanks may be used to further vary fuel rod axialdisplacement and diameter, allowing, for example, same-length fuel rodsto originate at different axial displacements from a lower tiered tieplate and terminate at a shared axial displacement at an upper flat tieplate. In this way thermo-hydraulic characteristics of exampleembodiment fuel bundles may be modified based on the verticaldisplacement of rods and/or shanks placed therein.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Example embodiments will become more apparent by describing, in detail,the attached drawings, wherein like elements are represented by likereference numerals, which are given by way of illustration only and thusdo not limit the example embodiments herein.

FIG. 1 is an illustration of a related art fuel assembly having flat tieplates affixed to fuel rods with shared vertical positions.

FIGS. 2A and 2B are illustrations of conventional flat upper and lowertie plates.

FIG. 3 is an illustration of an example embodiment tiered tie plateuseable as a lower tiered tie plate.

FIG. 4 is an illustration of an example embodiment tiered tie plateuseable as an upper tiered tie plate.

FIG. 5 is an illustration of an example embodiment fuel assembly using alower tiered tie plate.

FIG. 6 is an illustration of a shank useable with example embodimentfuel assemblies and tiered tie plates.

FIG. 7 is an illustration of an example embodiment fuel assembly using alower tiered tie plate with shanks.

FIG. 8 is an illustration of an example embodiment fuel assembly usingan upper tiered tie plate with shanks.

DETAILED DESCRIPTION

Detailed illustrative embodiments of example embodiments are disclosedherein. However, specific structural and functional details disclosedherein are merely representative for purposes of describing exampleembodiments. The example embodiments may, however, be embodied in manyalternate forms and should not be construed as limited to only exampleembodiments set forth herein.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of example embodiments. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element is referred to as being“connected,” “coupled,” “mated,” “attached,” or “fixed” to anotherelement, it can be directly connected or coupled to the other element orintervening elements may be present. In contrast, when an element isreferred to as being “directly connected” or “directly coupled” toanother element, there are no intervening elements present. Other wordsused to describe the relationship between elements should be interpretedin a like fashion (e.g., “between” versus “directly between”, “adjacent”versus “directly adjacent”, etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the languageexplicitly indicates otherwise. It will be further understood that theterms “comprises,” “comprising,” “includes,” and/or “including,” whenused herein, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

It should also be noted that in some alternative implementations, thefunctions/acts noted may occur out of the order noted in the figures.For example, two figures shown in succession may in fact be executedsubstantially concurrently or may sometimes be executed in the reverseorder, depending upon the functionality/acts involved.

FIG. 3 illustrates an example tiered tie plate 100 useable as a lowertiered tie plate. As shown in FIG. 3, example embodiment tiered tieplate 100 may include a body 115 having an inlet 110 configured to allowfluid coolant and/or moderator to pass into and through the body 115 ofexample tiered tie plate 100. Inlet 110 may take on a variety ofconfigurations based on the application; for example, inlet 110 mayinclude positioning and holding elements 112, shaped as hoops, that mayretain the example embodiment tiered tie plate in a specific orientationand position relative to the core and other fuel structures. Inlet 110may connect to a nozzle 111 that permits fluid flow to pass into amidsection 113. Midsection 113, while shown as hexahedral in FIG. 3, maybe shaped in any form depending on the application and may includeconventional flow-mixing and conditioning equipment. Inlet 110, nozzle111, and midsection 113 may make up the body 115 of example embodimenttiered tie plate 110.

Example embodiment tiered tie plate 100 further includes bosses 120defining holes shaped to receive ends or end plugs of nuclear fueluseable with example embodiment tiered tie plates. In this embodiment,the bosses 120 are annular. Axial support members 130 may connect thebosses 120 to each other and to the body 115 of the example embodimenttiered tie plate 100. Some bosses 120 may be integrated into the body115 midsection 113. Lateral support members 135 may connect the bosses120 to each other in a transverse direction perpendicular to the axial(vertical) direction. The bosses 120 may be spaced at a desiredinterval. For example, bosses 120 may be spaced in a square latticeformation with axial and lateral support members 130 and 135 extendingat least transversely from each boss 120 at 90-degree intervals, asshown in FIG. 3, or bosses 120 and support members 130 and 135 may bespaced radially, triangularly, etc., depending on where fuel rods may beplaced in the assembly. Similarly, bosses 120 and support members 130and 135 are not necessarily spaced at regular intervals. Bosses 120 andaxial and lateral support members 130 and 135 may be omitted over largerintervals to allow for other components or flow to pass through exampleembodiment tiered spacer 100. For example, some or all bosses 120 may beomitted, resulting in intersecting members 130 and 135, and analternative fuel end plug may be used.

Axial and lateral support members 130 and 135 are shown with thintransverse profiles so as to form several flow areas through exampleembodiment tiered tie plate 100. In this way fluid may pass through theinlet 110 and out around the bosses 120. While support members 130 and135 are shown as thin extending members, any connection between bosses120 and body 115 that permits flow through the example embodiment tieredtie plate may be used. As shown in FIG. 3, bosses 120 are positioned ata plurality of vertical (axial) displacements, called tiers. At a firstvertical displacement is tier 150, at a second vertical displacement istier 160, and at a third vertical displacement is tier 170. Each tier150, 160, and 170 may contain a plurality of bosses 120, so thatdifferent bosses 120 occupy different tiers 150, 160, or 170. Axialsupport members 130 may permit bosses 120 to occupy different verticaldisplacements by extending diagonally in both a transverse and axialdirection. For example, axial support members 130 may have aparallelogram cross-section, as shown in FIG. 3.

Although three different tiers are shown in FIG. 3, example embodimenttiered tie plates may include more distinct tiers, limited only by thenumber of bosses 120, such that each boss 120 may have its own tier.Further, although FIG. 3 shows tiers 150, 160, and 170 each havingbosses 120 continually and laterally joined in a square pattern bylateral and axial support members 130 and 135, tiers in exampleembodiment plates need not have all continuous and/or joined bosses 120.

By locating bosses 120 at different tiers of vertical displacement,example embodiment tiered tie plates may receive and hold nuclear fuelat several different axial displacements relative to each other. Severaldifferent three-dimensional configurations of bosses 120 and fuel rodsmay be possible with example embodiment tiered tie plates, due to theability of the bosses 120 to be placed at any combination of differenttransverse and axial positions.

FIG. 4 is an illustration of another example embodiment tiered tie plate200 that may be used as an upper tiered tie plate. As shown in FIG. 3,example embodiment tiered tie plate 200 may share several elements withpreviously described example embodiment tiered tie plate 100, whoseredundant description is omitted. Tiered tie plate 200 may includebosses 220 joined by axial and lateral support members 230 and 235similar to the description of FIG. 3. Also, bosses 220 may be at aplurality of different axial displacements, or tiers, 250, 260, or 270.

However, example embodiment tiered tie plate 200 may lack any body orlower inlet, and fluid may flow through and around bosses 220 andsupport members 230 and 235. Example embodiment tiered tie plate 200 mayinclude a handle 240 to facilitate handling and moving exampleembodiment fuel bundles including example embodiment tiered tie plate200.

FIG. 4 shows example embodiment tiered tie plate 200 having three tiers250, 260, 270 with different axial displacements and a square lattice ofbosses 220 at each tier. Tiers 250, 260, and 270 may correspond inrelative axial displacement and boss position to tiers 150, 160, and 170and their associated boss 120 position. In this way, as described below,example embodiment fuel bundles may use two example embodiment upper andlower tiered tie plates 200 and 100 with several fuel elements or rodsof a single length, with each rod equally seating in bosses 120 and 220of example embodiment tiered tie plates.

Example embodiment tiered tie plates may be fabricated from a materialthat provides sufficient material strength to support fuel rods indifferent axial positions with bosses 120/220 and support members130/135/230/235 and that substantially retains its physicalcharacteristics in an operating nuclear reactor environment. Forexample, zirconium-aluminum alloys, stainless steel alloys, etc., may beused to fabricate example embodiment tiered tie plates.

As shown in FIG. 5, example embodiment fuel assembly 300 may use exampleembodiment tiered tie plates 100 and 200 as lower and upper tie plates,respectively. Several fuel rods 310 may seated at both ends in exampleembodiment tiered tie plates 100 and 200, such that the tie plates 100and 200 join the fuel rods 310 together and to the example embodimentassembly 300. Other fuel rod designs and conventional features, such asspacers and end plugs, may be used in conjunction with exampleembodiment fuel assembly 300.

Because example embodiment tie plates 100 and 200 may have complementarytiers and bosses, fuel rods 310, while rigidly attached to fuel assembly300, may be at different axial displacements corresponding to thedifferent tiers of example embodiment tiered tie plates 100 and 200 asdescribed above. Further, fuel rods 310 may all have a same length dueto the mirrored axial displacement configuration between exampleembodiment tie plates 100 and 200. In this way, example embodiment fuelassembly 300 may have various three-dimensional configurations for fuelrod 310 starting and terminating points at either end of the assembly.

Although example embodiment fuel bundles are shown with the samethree-tiered configuration described with respect to example embodimenttiered tie plates, different tier and different corresponding rodconfigurations may be used in example embodiment bundle designs,depending on the thermo-hydraulic and nuclear properties of the bundleto be affected.

Example embodiment fuel bundles may use less than two example embodimenttiered tie plates. Conventional flat tie plates may be used in examplebundles through the use of rod shanks or multiple length fuel rods thataccount for the difference between a conventional flat tie plate and anexample embodiment tiered tie plate.

An example shank 500 is shown in FIG. 6. Example shanks 500 may begenerally cylindrical so as to present a continuous exterior when joinedwith fuel rods in example embodiment fuel bundles. Alternatively,example shanks may have a variety of shapes depending on the fuel shapeand desired flow characteristics around example shanks. Example shank500 may have a receptive end 502 and an insertive end 501. Receptive end502 may join through several known connection means, including a screwand threaded hole, to a fuel rod. Insertive end 501 may be seated in anexample embodiment tiered tie plate or conventional tie plate in thesame manner that a fuel rod would so seat.

Example shank 500 may have a length 504 equal to a displacement betweentiers and a body of example embodiment tiered tie plates. In this way,example shanks may attach to some of the fuel rods seated at an oppositeend in example embodiment tiered tie plates and account for thedifferences in axial displacement and rod termination caused by thetiers. Conventional flat tie plates may then be equally seated againsteach example shank and fuel rod despite the different axialdisplacements of the rods.

Example shank 500 may have a diameter 503 that presents a continuousouter boundary with any fuel rod it may be attached to. Alternatively,diameter 503 may be decreased to less than that of any fuel rod attachedto example shank 500. In this way, example embodiment fuel bundles usingexample shanks 500 with smaller diameters may have decreased fluidcoolant pressure drop and require less pumping head. Diameter 503 may bevaried and shaped in other ways depending on the desiredthermo-hydraulic characteristics of example embodiment fuel bundles.

FIG. 7 shows an example embodiment fuel bundle 600 using one exampleembodiment tiered tie plate 100 as a lower tie plate and a conventionalor otherwise flat upper tie plate 610. Fuel rods 620 may be positionedbetween the two tie plates 100 and 610. Because example embodimenttiered tie plate 100 may have varied vertical displacement of its bossesand corresponding starting position of lower fuel rods 620, fuel rods620 may terminate at different vertical displacements. Example shanks500 may compensate for these differing terminal vertical displacementsin the fuel rods 620 and present a planar termination at flat tie plate610. In this way, example embodiment fuel bundles may use fuel rods of asingle length with example embodiment tiered tie plate as a lower tieplate while still presenting a conventional flat upper tie plate forcompatibility with conventional core structures requiring a flat uppertie plate. Also, as shown in FIG. 7, diameters of example shanks 500 maybe varied throughout the example bundle 600.

FIG. 8 shows another example embodiment fuel bundle 700 using oneexample embodiment tiered tie plate 200 as an upper tie plate and aconventional or otherwise flat lower tie plate 710. Similarly to FIG. 7,example shanks 500 may compensate for the axial differences betweenexample embodiment upper tiered tie plate and the lower flat tie plate.

Example embodiment fuel bundles may thus possess fuel rods thatoriginate and/or terminate at differing axial (or vertical)displacements. As such, fluid flow through example embodiment fuelbundles may not be subject to a dramatic pressure drop at exampleembodiment upper and lower tiered tie plates, because example embodimenttiered tie plates essentially present a larger flow cross-section.Further, example shanks of smaller diameters may decrease pressure dropby similarly increasing flow cross-section and hydraulic diameter. Inthis way, example embodiments may improve hydrodynamic flow propertiesthrough an operating nuclear core and reduce pumping energy consumed.

Example embodiments thus being described, it will be appreciated by oneskilled in the art that example embodiments may be varied throughroutine experimentation and without further inventive activity. Forexample, other fuel types, shapes, and configurations may be used inconjunction with example embodiment fuel bundles and tiered tie plates.Variations are not to be regarded as departure from the spirit and scopeof the exemplary embodiments, and all such modifications as would beobvious to one skilled in the art are intended to be included within thescope of the following claims.

1. A tie plate for use in a nuclear fuel bundle, comprising: a pluralityof annular bosses positioned in two tiers in a honeycomb matrix, eachboss being a cylindrical tube configured to receive an end of a nuclearfuel rod, the first tier of bosses, at a first axial displacement, beinga center tier of bosses positioned in rows that are uniform such thatbosses from a different axial displacement other than the first axialdisplacement are not located within the first tier rows, the second tierof bosses, at a second axial displacement that is different from thefirst axial displacement, being positioned in rows circumscribing thefirst tier of bosses, the rows of second tier bosses being uniform suchthat bosses from a different axial displacement other than the secondaxial displacement are not located within the second tier rows.
 2. Thetie plate of claim 1, wherein the first tier of bosses is patterned tobe one of a square and a rectangular cross-sectional shape.
 3. The tieplate of claim 1, wherein the tie plate is configured to be used as anupper tie plate.
 4. The tie plate of claim 3, further comprising: ahandle attached to the plurality of bosses, the handle configured topermit handling and movement of the tie plate.
 5. The tie plate of claim1, further comprising: axial supports connecting the first tier ofbosses to the second tier of bosses, each axial support extendingdownward from the second tier to the first tier with a first endconnected to a first boss of the first tier of bosses and a second endconnected to a second boss of the second tier of bosses.
 6. The tieplate of claim 5, wherein, the axial supports are plate-shaped, thefirst end of each axial support is connected along an entirelongitudinal length of the first boss and the second end of each axialsupport is connected along an entire longitudinal length of the secondboss.
 7. The tie plate of claim 6, wherein, each axial support has aparallelogram cross-sectional shape, each axial support extendsdiagonally, relative to a horizontal cross section of the tie plate,from the first tier to the second tier, the horizontal cross sectionexisting in a plane that is perpendicular to a fluid flow through thetie plate when the tie plate is in operation in the nuclear fuel bundle.8. The tie plate of claim 1, further comprising: a body connected to thefirst and second tiers of bosses; and an inlet extending below the bodyin an axial direction, the inlet configured to permit fluid flow intothe body, the bosses, the axial supports and the lateral supportsdefining spaces between the bosses to permit the fluid flow through thebody.
 9. The tie plate of claim 8, further comprising: additional tiersof annular bosses, at additional axial displacements that are differentfrom the first and second axial displacements, being positioned in rowscircumscribing the second tier of bosses.
 10. The tie plate of claim 8,further comprising: a plurality of third tier annular bosses, at a thirdaxial displacement, embedded in the body, the third axial displacementbeing at an axial displacement that is different from the first axialdisplacement, the second axial displacement and the additional axialdisplacements.
 11. The tie plate of claim 5, further comprising: aplurality of first lateral supports, each of the first tier bosses beingconnected to at least two lateral supports, each of the first lateralsupports connected to two of the first tier bosses; a plurality ofsecond lateral supports, each of the second tier bosses being connectedto at least two lateral supports, each of the second lateral supportsbeing connected to two of the second tier bosses.
 12. A tie plate for usin a nuclear fuel bundle, comprising: a plurality of annular bossespositioned in two tiers in a honeycomb matrix, each boss being acylindrical tube configured to receive an end of a nuclear fuel rod, thefirst tier of bosses having a first axial displacement, the second tierof bosses having a second axial displacement that is different from thefirst axial displacement; and axial supports connecting the first tierof bosses to the second tier of bosses, each axial support extendingdownward from the second tier to the first tier with a first endconnected along an entire longitudinal length of a first boss of thefirst tier of bosses and a second end connected along an entirelongitudinal length of a second boss of the second tier of bosses. 13.The tie plate of claim 12, wherein the axial supports are plate-shaped.14. The tie plate of claim 13, wherein, each axial support has aparallelogram cross-sectional shape, each axial support extendsdiagonally, relative to a horizontal cross section of the tie plate,from the first tier to the second tier, the horizontal cross sectionexisting in a plane that is perpendicular to a fluid flow through thetie plate when the tie plate is in operation in the nuclear fuel bundle.15. The tie plate of claim 12, wherein, the first tier of bosses is acenter tier of bosses positioned in rows that form one of a square and arectangular cross-sectional shape, the second tier of bosses arepositioned in rows circumscribing the first tier of bosses.
 16. The tieplate of claim 15, further comprising: additional tiers of annularbosses, at additional axial displacements that are different from thefirst and second axial displacements, being positioned in rowscircumscribing the second tier of bosses.
 17. A tie plate for us in anuclear fuel bundle, comprising: a plurality of annular bossespositioned in two tiers in a honeycomb matrix, each boss being acylindrical tube configured to receive an end of a nuclear fuel rod, thefirst tier of bosses, at a first axial displacement, being a center tierof bosses positioned in rows, a plurality of first lateral supports,each of the first tier bosses being connected to at least two lateralsupports, each of the first lateral supports connected to two of thefirst tier bosses; the second tier of bosses, at a second axialdisplacement that is different from the first axial displacement, beingpositioned in rows circumscribing the first tier of bosses; a pluralityof second lateral supports, each of the second tier bosses beingconnected to at least two lateral supports, each of the second lateralsupports being connected to two of the second tier bosses.
 18. The tieplate of claim 17, wherein the lateral supports are plate-shaped with afirst and second end each connected to an entire longitudinal length ofa respective annular boss.
 19. The tie plate of claim 18, furthercomprising: axial supports connecting the first tier of bosses to thesecond tier of bosses, each axial support extending downward from thesecond tier to the first tier with a first end connected to an entirelongitudinal length of a first boss of the first tier of bosses and asecond end connected to an entire longitudinal length of a second bossof the second tier of bosses.
 20. The tie plate of claim 19, furthercomprising: additional tiers of annular bosses, at additional axialdisplacements that are different from the first and second axialdisplacements, being positioned in rows circumscribing the second tierof bosses.